(CNN) -- "Listen, we're all *possibly* Frank Sinatra's son," Ronan Farrow tweeted last week.
The lighthearted message masterfully sidestepped gossip and scandal: His mother, actress Mia Farrow, divulged to Vanity Fair magazine that ex-husband Frank Sinatra could "possibly" be the 25-year-old's father. It was long believed that the biological father of the Rhodes Scholar-turned-diplomat-turned-lawyer was filmmaker Woody Allen, who had a relationship with Farrow for 12 years.
Ronan Farrow fell out with Allen when it came to light that the prolifically quirky director was having an affair with one of Mia Farrow's adopted daughters, Soon-Yi Previn. Allen and Previn later married in 1997. On Father's Day last year, Ronan memorably tweeted: "Happy Father's day -- or as they call it in my family, happy brother-in-law's day."
While this most recent questioning about paternity made headlines because of the famous parents, the circumstance can shake any family, according to psychology experts. Families shaped by divorce and remarriage, traditional adoption, second-parent adoption, surrogacy and in vitro fertilization might mean the conversation happens more often than ever before.
'The world opened up'
For Brian Hansen, 32, of New Jersey, his life changed over a drink with a cousin in 2010.
Hansen and his wife were expecting their first child, and he told his cousin he was scared of the type of parent he would be because of the angry father he had known.
"My cousin saw that I was very worried and in a distressed place," Hansen said.
His cousin, sensing his angst, figured it was time to come clean: The man who had raised Hansen was not his biological father. Hansen's mother had used a sperm donor to conceive both him and his younger sister.
"I just sat there and stared at him for nine or 10 seconds," Hansen said.
"... My life literally re-defined by fermented oats served cold by a waitress with nose jewelry named Miranda," he wrote on his blog less than 24 hours later in a post titled "And Now For Something Completely F***ed."
For Hansen, there was an immediate sense of relief. From about age 7, Hansen said he and his sister would look at each other and ask: "Where did we come from?"
He had a rocky relationship with his father growing up, and in 2008, he severed ties once and for all. His parents, now divorced, were together for 32 years.
"Once I found out I wasn't beholden to his gene, the world opened up," Hansen said.
While Hansen's and Ronan Farrow's paternal relationships fell into the "strained" camp, experts such as Jennifer Hogan say the news can rock a family whether the parent-child relationship is good, bad or downright ugly. This type of news will raise issues of identity and trust, especially if other family members were in on the secret.
"It shakes your self-awareness and sense of self to its core," said Hogan, a licensed clinical social worker. "For parents, the important thing to understand is that we get a lot of identity from who our immediate family is."
Think about it: Recreational hobbies, personality traits, even career paths often follow the suit of a parent.
"The child starts to feel like an outsider to their family," Hogan said.
Hogan said Hansen's sense that he "wasn't destined to become the same as this person" can be freeing: "You get a clean slate for half of your biology."
But there will also be some uncertainty about what traits might come from a newly discovered parent.
"It will shake your foundation," Dr. Gabriela Cora agrees. "Even if you suspected it before, confirming it can still be a shocker."
'Secrets are inherently destructive'
For parents, of course, the million-dollar question is when to deliver the news.
"Secrets are inherently destructive to families," Hogan said. "Eventually they come out, and they cause a lot of havoc."
The debate over disclosure versus secrecy is one that adoption support groups advise should be ongoing within families -- and that the child's age and inquisitiveness are cues for how much to make known. There's no easy answer.
"Adult adoptees who grew up with secrecy talk about feeling that something wasn't 'right' about them, about feeling both betrayed and relieved when they learned the truth. Others interpreted their parents' reluctance to talk to mean that adoption was taboo," Lois Melina wrote in Adoptive Families magazine.
Cora, a psychiatrist, encourages the same process for all parents who aren't biologically linked to their child. "Err on being truthful," she said.
A big factor in the "when" is if the children are old enough to comprehend the implications or if they start raising questions about their identity, Cora said.
If the child is really young and determined to seek out a biological tie that isn't part of his or her current life, the parents who raised the child might encourage him or her to wait a couple of years to seek out roots -- and agree to help when the time comes.
Hogan said innately understanding where you come from is something children begin to want to understand. But the age at which it's discussed should be when they can steel themselves for rejection.
"It is the ultimate rejection if your biological parent doesn't have interest in you," she said.
Hogan suggests parents be honest in their explanations, acknowledging their own fears and doubts about telling the truth. This is especially pertinent if a child could have been abused, mistreated or neglected in the care of a biological parent.
"People think that they really want to know the truth (about their biological parents), but they've idealized that truth," Cora said.
The child, even as an adult, will discover and decide for him or herself what comes from nature and what's nurtured.
For Hansen, who had a rough relationship with his dad, he said he felt a release of issues he thought were innate.
But he was upset that his mother didn't tell him the truth while he dealt with his own anger issues, or when he and his wife asked about medical history before trying to have a baby. With a lot of processing -- therapy, that is -- his relationship with his mother is at a peaceful point, he said.
"She thought she was doing the right thing by not telling us, and in her view, he loved us, she loved us, they were our parents -- and none of the other stuff mattered," he said.
"Because of the way that I was raised, he's always going to be a part of who I am -- biological or not."